This invention relates to pumps for pumping liquids, and more particularly to a pump assembly having added leak protection.
One type of pump available at present includes an impeller casing having a fluid inlet and a fluid outlet with an impeller located within the casing for moving the fluid through the casing from the inlet to the outlet. The impeller is mounted on and rotated by a shaft which is driven by a motor externally of the impeller casing, with the shaft penetrating the impeller casing. The shaft and impeller carried thereby are supported by bearings which are located within a bearing housing which provides for lubrication of the bearings. The impeller casing is attached to the bearing housing by an adaptor. This "modular" arrangement provides substantial flexibility by permitting many pump assemblies with different operating parameters to be produced by combining different impeller assemblies and bearing assemblies. The number of parts stocked by a manufacturer is greatly reduced while a large number of different pump assemblies can be provided.
The impeller casing has a seal at its driven end which, for example, may include a seal or packing and an appropriate gland. This seal prevents leakage of the liquid being pumped by the pump. The bearing housing has inboard and outboard seals to prevent lubricating oil from leaking from the bearing housing. Because of the "open-back" construction, failure of either one of the seals will result in leakage of the fluid being pumped or bearing lubrication oil, requiring shutdown of the pump and disruption of the pumping process until the leakage can be repaired. Because the pump must be shut down as soon as the leakage is detected, the repair cannot be scheduled prior to shutting down of the pump.
Recently, the Environmental Protection Agency has issued more stringent standards for pumps which are used to pump certain hazardous fluids. For example, the standards for light liquid service require dual mechanical seal systems and a barrier fluid system with each dual mechanical seal system. Also, the barrier fluid system must be operated with the barrier fluid at a pressure that is at all times greater than the pump stuffing box pressure or equipped with a barrier fluid degassing reservoir that is connected by a closed-vent system to a control device. An alternative requirement is that the pump be designed with no externally actuated shaft penetrating the impeller casing.
Accordingly, it would be highly desirable to have a pump assembly which includes the flexibility of existing modular pump assemblies, but which is further characterized by improved protection against leakage and is well suited to meet the new regulations being issued by the Environmental Protection Agency.